1. Field of the Invention
This invention relates to structural laminates and foam filled sheet products and more particularly it relates to structurally rigid sheets of foam having a glass fibers distributed substantially evenly throughout the foam. It also relates to a method for forming such a product.
2. Description of the Prior Art
Many attempts have been made to create structural laminates particularly of foamed resins to be used as low density thermal insulation and particularly decorative wall and ceiling panels in metal buildings. Before laminates of this type can be used, however, it is necessary that they meet certain fire safety standards. In particular, when installed in a structure, the material of the laminate when subjected to an open flame should not produce a self-propagating fire within the limits of the structure as evidenced by flaming or material damage. See "Acceptable Performance Criteria, Factory Mutual Building Corner Fire Test Procedure."
Recently a new generation of polymer foam materials have appeared in which the isocyanurate moiety is the major recurring chemical unit. These materials have much greater stability and resistance to heat than do previous foamed resins such as the polyurethanes. Further, the resistance is achieved without the use of any significant amounts of fire retardant additives. The smoke generated by combustion of these materials is much smaller in volume than that generated by combustion of an equivalent amount of other foams and is relatively free of toxic components typically generated by combustion of conventional halogen and/or phosphorus containing fire retardant additives. An example of a laminate of this type using polyisocyanurate as core material is to be found in U.S. Pat. No. 3,814,659. The discussion concerning the foam core found in Columns 4 and 5 of that patent is particularly noteworthy.
While it has been recognized that polyisocyanurates have some superior qualities to previously known foams, common difficulties with other foams still remain, particularly, the flammability of the foam when subjected to a fire of sufficient intensity and heat. Sudden exposure to conditions of high temperature and open flame is known to result in surface charring of a polyisocyanurate foam which tends to limit the surface spread of flame and retard the involvement of the sub-surface foam. However, local structural failure of the foam under these exposure conditions frequently leaps to increased surface exposure, total involvement of the foam core and a self-propagating fire.
It is therefore an object of this invention to create a structural laminate having superior fire resistant properties which would qualify for approval by the Factory Mutual Research Corporation, an independent risk certification firm.
It is a further object of this invention to form a structural laminate utilizing a superior polyisocyanurate resin with a mat of long straight glass fibers to form a unique laminated thermal insulation of superior performance and of pleasing appearance.
Previous attempts to make similar structures utilizing foams other than polyisocyanurate have relied on the spongy character of a high loft batting into which a foam-forming resin was forced and then permitted to foam and expand at the same rate as the high loft fiberous batting material expanded. An example of this process applied to making a flexible foam filled batting material can be found in U.S. Pat. No. 3,617,594.
A distinct disadvantage is presented by using a high loft batting in that the batting may elastically recover faster than the foam forming mixture expands thereby producing voids or pockets within the resultant material, the pockets contributing directly to possible structural failure of the material when subjected to high heat conditions.
It is therefore an object of this invention to form a structural laminate using a low loft mat of long straight glass fibers, the mat being thin, substantially incompressible, yet expansible under the sole influence of the expansion of a foam-forming mixture which penetrates and completely fills the interstices between the fibers of the mat.
A method of making a low loft mat which satisfies the functional and structural requirement of this invention is to be found in U.S. Pat. No. 2,609,320 provided certain limitations are placed on the method. For example, in a mat acceptable for use in a laminate according to this invention, the glass fibers are attached to one another by an amount of fiber binder sufficient to make the mat of glass fibers dimensionably stable but insufficient to fill the interstices between the glass fibers. Preferably only a minimum amount of this fiber binder should be employed. Further the mat should not be expanded or puffed up in thickness as it taught in U.S. Pat. No. 2,609,320 but rather should be of low loft such that pressured applied to the faces of the mat will not substantially reduce the thickness of the mat and such that the mat does not elastically recover to any appreciable amount when the structure is released from the faces of the mat. Of course, any other method can be used which would result in a batt of glass fibers having a structure substantially the same as that produced by the method of U.S. Pat. No. 2,609,320 with these restrictions.